Impact of linker functionalization on the adsorption of nitrogen-containing compounds in HKUST-1

Construction of 2D zinc(II) MOFs with tricarboxylate and N-donor mixed ligands for multiresponsive luminescence sensors and CO2 adsorption

The solvothermal reactions of ZnCl2·6H2O, benzene-1,3,5-tribenzoic acid (H3btb), and N-heterocyclic ancillary imidazole (Im) or aminopyrimidine (a mp) ligands led to the creation of two-dimensional (2D) zinc(II) based metal-organic frameworks (MOFs), (Me2NH2)2[Zn2(btb)2(Im)2]·2DMF·3MeOH (1) and (Me2NH2)2[Zn2(btb)2(amp)]·H2O·2DMF·MeOH (2). The btb3- ligands in 1 and 2 form an anionic 2D layered structure with a (63) honeycomb (hcb) topology by linking to Zn(II) centres through their carboxylate groups. The incorporation of N-heterocyclic auxiliary ligands Im and amp into the hcb nets resulted in the formation of a 2D hydrogen-bonded and covalently pillared bilayer structure featuring two-fold interpenetrating networks. Each of these networks consists of small channels that are occupied by Me2NH2 cations and solvent molecules. Both 1 and 2 emit blue luminescence emissions in the solid state at room temperature and exhibit a great selectivity and sensitivity for the detection of acetone and multiple heavy metal ions including Hg2+, Cu2+, Fe2+, Pb2+, Cr3+, and Fe3+ ions. At 1 bar, activated 1 and 2 demonstrate moderate capacities for adsorbing CO2 at room temperature, with a preference for CO2 over N2. Notably, at higher pressures (up to 20 bar), their activated samples 1 and 2 show a temperature-dependent enhancement of CO2 uptake while retaining good stability.

The surface structure, stability, and catalytic performances toward O2 reduction of CoP and FeCoP2

The systematic atomistic level investigation of low-index surface structures, stabilities, and catalytic performances of CoP and FeCoP₂ towards the O₂ reduction reaction (ORR) is vital for their applications. Employing first-principles calculations, it is revealed that CoP and FeCoP₂ present the same surface stability in the order of (101) ≈ (011) > (111) > (001) > (110) > (010) > (100). They also possess a similar Wulff equilibrium crystal shape with (101) and (011) exposing the largest surface area. From the electronic view, FeCoP₂ presents improved electronic conductivity compared with CoP. From the energy view, whether FeCoP₂ delivers improved electrocatalytic activity toward the ORR with respect to CoP depends on the reactive surfaces and sites. Among the 4 surfaces considered, only CoP(101), FeCoP₂(101) and FeCoP₂(011) delivered ORR performances theoretically when the bridge metal-metal site acts as the reactive center, which makes CoP(011) the only exception. CoP(101)-b_Co-Co and FeCoP₂(011)-b_Fe-Co exhibit a larger thermodynamic limiting potential than FeCoP₂(101)-b_Co-Co, suggesting their higher performances toward the ORR. The last step of HO* desorption as the rate-limiting step accounts for 3/4. The third step of transformation from O* to HO* as the most sluggish step accounts for 1/4. The work function, d-band center, Bader charge, and electronic localization function calculations are performed to reveal the HO adsorption nature. The present work provides fundamental insight into the effect of Fe doping into CoP, the determination of the catalyst surface and the key species adsorption nature to guide the rational design of high-performance materials.

Modulating the Biomimetic and Fluorescence Quenching Activities of Metal-Organic Framework/Platinum Nanoparticle Composites and Their Applications in Molecular Biosensing

Nanoscale metal-organic frameworks (nMOFs) have gained considerable attention with significant potential applications. Although great efforts have been devoted to designing and fabricating nanoscaffold structures, approaches of deliberately regulating the intrinsic functionality of nMOFs have been poorly explored. Herein, we report a simple and novel strategy to regulate the catalytic and fluorescence quenching behaviors of nMOFs through coordination-driven self-assembly. As a proof-of-concept, we synthesized a synergistic and stable MOF-metal nanocomposite by loading platinum nanoparticles (PtNPs) on a commonly used Fe-MOF, i.e., MIL-88B-NH₂/Pt, as a MOF composite model for exploration. On one hand, the complexation with ATP effectively broke the pH limitation of the peroxidase-mimicking MIL-88B-NH₂/Pt nanozyme, bringing a 10-fold increased catalytic activity under alkaline condition. Based on the distinct catalytic enhancement between ATP and other nucleotides, real-time monitoring of apyrase activity as well as colorimetric detection of alkaline phosphatase (ALP) was performed. On the other hand, interactions of MIL-88B-NH₂/Pt with fluorescent DNA were tolerant of different nucleic acids and, more importantly, were further manipulated by inorganic molecules. As a result, H₂O₂ could only trigger the release of a G-rich sequence, while phosphates could readily induce desorption of various DNA molecules with varying lengths, sequences, and fluorescent dyes. Accordingly, fluorescent DNA and MIL-88B-NH₂/Pt as functional probe-quencher pairs were proposed, allowing the establishment of a fluorescence bioassay for ALP and PPase detection and Boolean logic calculations. This work offers a means to tune the intrinsic activities of nMOFs by surface engineering, benefiting design of functional nanomaterials and development of advanced biosensing systems.

Simultaneous detection of dual biomarkers using hierarchical MoS2 nanostructuring and nano-signal amplification-based electrochemical aptasensor toward accurate diagnosis of prostate cancer

Accurate and reliable quantification of tumor biomarkers in clinical samples is of vital importance for early stage diagnosis and treatment of cancer. However, a poor specificity of prostate specific antigen (PSA) testing alone fostering overdetection and overtreatment, remains a great controversy in prostate cancer (PCa) screening. Here we report an electrochemical aptasensor using hierarchical MoS₂ nanostructuring and SiO₂ nano-signal amplification for simultaneous detection of dual PCa biomarkers, PSA and sarcosine, to enhance the diagnostic performance of PCa. In this strategy, hierarchical flower-like MoS₂ nanostructures as functional interface accelerated intermolecular accessibility and improved DNA hybridization efficiency. Moreover, the spherical SiO₂ nanoprobe that conjugated with both electroactive tags and DNA probes, allowed effective electrochemical signal amplification. By deliberately designing different hybridization modes, we individually implemented the optimization of PSA and sarcosine sensing system. Based on this, simultaneous determination of PSA and sarcosine was achieved, with limit of detection (LOD) down to 2.5 fg/mL and 14.4 fg/mL, respectively, as well as excellent selectivity. More importantly, using this approach, we could directly differentiate cancer patients with healthy ones for clinical serum samples. The ultrasensitive biosensor provides single-step analysis with simple operation and a small sample volume (∼12 μL), shedding new light on accurate diagnosis and early-detection of cancer in clinical applications.

“Three-in-One” Nanocomposite as Multifunctional Nanozyme for Ultrasensitive Ratiometric Fluorescence Detection of Alkaline Phosphatase

Nanozymes, as a unique class of nanomaterials with enzyme-like properties, have attracted significant interests due to their potential applications in many significant fields. Great endeavours have been devoted to improving...

Defect-Engineered NiCo-S Composite as a Bifunctional Electrode for High-Performance Supercapacitor and Electrocatalysis

Defect engineering is a reasonable solution to improve the surface properties and electronic structure of nanomaterials. However, how to introduce dual defects into nanomaterials by a simple way is still facing challenge. Herein, we propose a facile two-step solvothermal method to introduce Fe dopants and S vacancies into metal-organic framework-derived bimetallic nickel cobalt sulfide composites (NiCo-S). The as-prepared Fe-doped NiCo-S (Fe-NiCo-S) possesses improved charge storage kinetics and activities as electrode material for supercapacitors and the oxygen evolution reaction (OER). The obtained Fe-NiCo-S nanosheet has a high specific capacitance (2779.6 F g^-1 at 1 A g^-1) and excellent rate performance (1627.2 F g^-1 at 10 A g^-1). A hybrid supercapacitor device made of Fe-NiCo-S as the positive electrode and reduced graphene oxide (rGO) as the negative electrode presents a high energy density of 56.0 Wh kg^-1 at a power density of 847.1 W kg^-1 and excellent cycling stability (capacity retention of 96.5% after 10,000 cycles at 10 A g^-1). Additionally, the Fe-NiCo-S composite modified by Fe doping and S vacancy has an ultralow oxygen evolution overpotential of 247 mV at 10 mA cm^-2. Based on the density functional theory (DFT) calculation, defects cause more electrons to appear near the Fermi level, which is conducive to electron transfer in electrochemical processes. Our work provides a rational strategy for facilely introducing dual defects into metal sulfides and may provide a novel idea to prepare electrode materials for energy storage and energy conversion application.

Single-metal-atom catalysts supported on graphdiyne catalyze CO oxidation

Single-metal-atom catalysts supported on graphdiyne (GDY) exhibit great potential for catalyzing low temperature CO oxidation in solving the increasingly serious environmental problems caused by CO emissions due to the high catalytic activity, clear structure, uniform metal distribution and low cost. First principle calculations were employed to study CO oxidation activities of four M@GDY single-atom catalysts (M = Pt, Rh, Cu, and Ni). For each catalyst, five possible reaction mechanisms including bi-molecular and tri-molecular reactions were discussed. According to the calculated reaction barriers, the preferred reaction pathway is via the bi-molecular Langmuir-Hinshelwood (BLH) ((CO + O₂)* → OCOO* → CO₂ + O*) route to yield the first CO₂ molecule with 0.55, 0.51, and 0.53 eV as the energy barriers of the rate-limiting steps of Pt@GDY, Rh@GDY, and Cu@GDY, respectively, whereas for Ni@GDY, it switches to the tri-molecular Eley-Rideal (TER1) ((2CO)* + O₂→ OCOOCO* → 2CO₂) mechanism with the reaction barrier of the rate-limiting step being 1.27 eV. Based on the energy difference in the initial states of the five reaction mechanisms, TER1 is generally viable. No matter it is based on the calculated reaction barrier or the energy of the initial state of each mechanism, the non-noble Cu@GDY is supposed to be an efficient catalyst as the noble ones. The electronic properties are calculated to explain the bonding strength and origin of the catalytic performance. The GDY support plays an important role in the electron transfer process.

Construction of MOF-shell porous materials and performance studies in the selective adsorption and separation of benzene pollutants

Metastable Cu2O is an attractive material for the architectural design of integrated nanomaterials. In this context, Cu2O was used as the sacrificial agent to form the core-shell structure of Cu2O@HKUST-1 by in situ growth technology. The MOFs with BOPs adsorption property were gathered together by a Cu2O etching method, and the hollow structure of the HKUST-1 shell material with fast BOP adsorption was successfully constructed. The adsorption experiments showed that the HKUST-1 shell has a good adsorption effect on nitrobenzene pollutants in wastewater. The investigation of various factors affecting the adsorption, thermodynamic and kinetic equations was carried out. The adsorption equilibrium was reached within 30 min, and the maximum adsorption capacity was 94.67 mg g-1 at 298 K. The adsorption capacity of nitrobenzene by the HKUST-1 shell is in good agreement with the Freundlich model and the second-order kinetic model. The possible mechanism of adsorption of nitrobenzene by the HKUST-1 shell was discussed. The experimental results suggested that Cu-BTC materials have potential applications for wastewater treatment involving benzene pollutants.

Construction of Bio-Nano Interfaces on Nanozymes for Bioanalysis

Nanomaterials with enzyme-like activity (nanozymes) have been of great interest in broad applications ranging from biosensing to biomedical applications. Despite that much effort has been devoted to the development of the synthesis and applications of nanozymes, it is essential to understand the interactions between nanozymes and most commonly used biomolecules, i.e., avidin, streptavidin (SA), bovine serum albumin (BSA), immunoglobulin G (IgG), and glutathione (GSH), yet they have been rarely explored. Here, a series of bio-nano interfaces were constructed through direct immobilization of proteins on a variety of iron oxide and carbon-based nanozymes with different dimensions, including Fe₃O₄ nanoparticles (NPs, 0D), Fe₃O₄@C NPs (0D), Fe₃O₄@C nanowires (NWs, 1D), and graphene oxide nanosheets (GO NSs, 2D). Such interfaces enabled the modulation of the catalytic activities of the nanozymes with varying degrees, which allowed a good identification of multiplex proteins with high accuracy. Given the maximum inhibition on Fe₃O₄@C NP by BSA, we established molecular switches based on aptamer and toehold DNA, as well as Boolean logic gates (AND and NOR) in response to both DNA and proteins. Also importantly, we developed an on-particle reaction strategy for colorimetric detection of GSH with ultrahigh sensitivity and good specificity. The proposed sensor achieved a broad dynamic range spanning 7 orders of magnitude with a detection limit down to 200 pg mL^-1, which was better than that of an in-solution reaction-based biosensor by 2 orders of magnitude. Furthermore, we explored the mechanisms of the interactions at bio-nano interfaces by studying the interfacial factors, including surface coverage, salt concentration, and the curvature of the nanozyme. This study offered new opportunities in the elaborate design and better utilization of nanozymes for bioanalysis in clinical diagnosis and in vivo detection.

The Application of Metal-Organic Frameworks and Their Derivatives for Supercapacitors

Supercapacitors (SCs), one of the most popular types of energy-storage devices, present lots of advantages, such as large power density and fast charge/discharge capability. Being the promising SCs electrode materials, metal-organic frameworks (MOFs) and their derivatives have gained ever-increasing attention due to their large specific surface area, controllable porous structure and rich diversity. Herein, the recent development of MOFs-based materials and their application in SCs as the electrode are reviewed and summarized. The preparation method, the morphology of the materials and the electrical performance of various MOFs and their derivatives (such as carbon, metal oxide/hydroxide and metal sulfide) are briefly discussed. Most of recent works concentrate on Ni-, Co- and Mn-MOFs and their composites/derivatives. Conclusions and our outlook for the researches are also given, which would be a valuable guideline for the rational design of MOFs materials for SCs in the near future.